This blog discusses current weather, weather prediction, climate issues, and other topics

Wednesday, June 3, 2015

Unusual Early Season Lightning But Few Fires

There has been an extraordinary amount of lighting during the last week or so....far more than usual this early in the season. Let me show you with a series of maps showing 24-h lightning totals over the region. These are from the NLDN lightning detection network.

May 23: Over and east of the Cascades

May 24th: Lots over the Cascades as cumulonimbus clouds developed over and east of the crest.

How could this be? Because the ground is too moist. The Standardized Precipitation Index from the National Drought Mitigation Center for the last month shows the story: wetter than normal east of the Cascade crest due to all the rain from incessant convection in that region. Southwest of our region it has been crazy wet.

The latest NOAA Climate Forecast System (CFSv2) runs for the summer indicates wetter than normal conditions expected for the interior.

Why has the region east of the Cascades been so wet? Because the large scale atmospheric circulation has been anomalous. To illustrate this, here is difference from normal (climatology) of the heights of the 500 hPa pressure surface (you can think of it like the pressure pattern at around 18,000 ft). There was anomalously low pressure over the SW U.S. and nigh pressure over the Gulf of Alaska. This pattern brought enhanced easterly flow over region, with moisture circulating westward. This pattern has brought unusually heavy precipitation over the SW US, including Texas.

All of this shows why one has to be very careful in predicting a disastrous early wildfire season based on low snowpack: temperature and moisture are much more important. But eventually, the ground will dry out and wildfires will return. The models are predicting warmer than normal conditions for the summer, which would enhance wildfire potential. But they are also wetter than normal. That works against wildfires. But if much of that rain is from thunderstorms, that might enhance wildfire potential. To put it another way, there is a lot of uncertainty in the wildfire outlook. We need to be prepared.

5 comments:

When I lived in Central Arizona, I grew to love the (almost) realtime lightning maps (with sound!) at www.lightningmaps.org/realtime?lang=en (currently has a 7s delay and is showing some quite active storms over eastern Wyoming and Montana and another set over Kansas.)

Cliff said: "All of this shows why one has to be very careful in predicting a disastrous early wildfire season based on low snowpack: temperature and moisture are much more important."

Well, this is a slightly off-the-mark conclusion that misses the better question: Are we talking wildfire frequency or wildfire intensity? The damp weather has indeed kept the Inland Empire from starting Fire Season so soon after Memorial Day Weekend, but it has merely inverted the problem areas elsewhere, at least in the case of Oregon. As of earlier this week, we have had a total of 113 Non-Industrial Wildfires with 16 Industrial Activity (Logging) Wildfires. The majority of these have actually been west of the Cascades, and each individual fire has been relatively small. So, we're at ~130 fires for 2015 so far, and this is up from about 80 as of 3 weeks ago. At that time, a colleague of mine in Oregon Department of Forestry stated that we were "above average" for activity, since we average 50 fires heading into Memorial Day Weekend annually.

My point is that Fire Season is already here, it is just being observed on smaller scales over a wider scope of landscape than what the Northwest equates with summer wildfires. Considering much of the region is under some level of drought, this will affect the spatial distribution of fire activities just as much, if not more, than the temporal distribution.

Yesterday afternoon there were very big, dark clouds forming over the eastside (Kirkland, Redmond) and then again over the Olympics. I ride my bike home so I was checking out the radar. But there was nothing on the radar. Why would that be? Were the clouds too low? Or too dry? Just curious. Thanks.